Heating mechanism for warming the ink in the write head of an ink printer means

ABSTRACT

In an ink jet printer, the ink is warmed by a heating device comprising a temperature sensor element and a voltage regulator component as a heating element, this being arranged on the write head carrier; the heating element is supplied with a constant load current via a regulating circuit until an adjustable operating temperature is reached; the heating energy for warming the ink is offered via the dissipated heat of the heating element.

The invention is directed to a heating mechanism for warming the ink inthe write head of an ink printer means wherein the wire head comprises aplurality of ink channels ending in discharge openings and comprisingindividually drivable, electrothermal transducer elements allocated toevery ink channel under whose influence the ink in the region of atransducer element in the ink channel is suddenly heated until an inkvapor bubble is formed, and, in particular, whereby the write head isarranged in a write head carrier that is large in area in comparison tothe write head.

A known principle for portraying characters on a recording medium isbased upon ejecting individual ink droplets from the nozzles of a writehead that is a component part of an ink printer means the ink drops,being ejected therefrom under the influence of a control means.Characters and/or graphic patterns are constructed grid-like on therecording medium by coordinating the ejection of individual droplets andthe relative motion between the recording medium and the write head. Theoperational reliability and the quality of the recording are highlydependent on the uniformity of the droplet ejection, i.e. the individualdroplets ejected by a drive pulse must have a defined size and mustleave the nozzle of the write head with the respectively same speed. Theinfluence of the viscosity of the ink is extremely critical for auniform droplet ejection. This is highly dependent on the temperature.It is therefore already known to hold the temperature of the ink in anink printer head a constant value. It is known (in German PublishedApplication 26 59 398 for example) to provide a heating element in thenozzle plate for a write head wherein individual ink channels areprovided that end at discharge nozzles of a nozzle plate. It is alsoknown for such write heads to provide an induction coil in the region ofthe nozzle plate and heat to the nozzle plate by eddy currents andhysteresis losses (in German Published Application 35 00 820) forexample.

It has recently been disclosed to achieve the ejection of individual inkdroplets in that an ink vapor bubble is produced in the region of anelectrothermal energy transducer arranged in the ink channel, this inkvapor bubble ejecting a defined ink volume from the ink channel as adroplet. Such write heads can be constructed using what is referred toas thin-film technology. The temperature dependency cf the viscosity ofthe ink is also a very critical factor for write heads of this type. Itis therefore also known for write heads of this type to improve theejection conditions by warming the ink fluid. This can occur byadditional heating elements acting on the ink from the outside (forexample, see German Published Application 29 43 164 and German PublishedApplication 35 45 689). PTC resistors are employed as heating elementsfor this purpose. The temperature of the ink in the write head can thusbe brought to a defined value and held at said defined value incombination with a regulating circuit and with a temperature sensorelement for which, for example, a high-temperature conductor or a PTCresistor can be utilized. Particularly in write heads havingelectrothermal transducers, however, relatively long heating timesderive since the heating elements are superficially arranged on a writehead carrier that is designed relatively bulky or, respectively, largein area. The reason for this is that measures for cooling must beprovided under certain circumstances for write heads with electrothermaltransducers because of the warming of the ink occurring during anongoing printing operation. The write head is usually arranged on analuminum plate for this purpose that serves as a cooling member. Whenthe ink must be warmed upon turn-on, given operation with few nozzles orafter longer-lasting printing mode of the ink printer means, the coolingmember must then also always be heated as well.

Although it is already known (in German Published Application 29 43164), for example, to arrange a heating coil in the interior of the inkspace, this involves considerable structural outlay. Over and abovethis, additional problems arise because of chemical processes that occurbetween the coil material and the ink fluid.

It is an object of the invention to specify an arrangement for warmingor, respectively, for heating the ink for a write head in ink printerequipment comprising a plurality of ink channels ending in dischargeopenings and comprising individually drivable, electrothermal transducerelements allocated to every ink channel under whose influence the ink inthe region of a transducer element in the ink channel is suddenly heateduntil the formation of an ink vapor bubble, whereby the write head isarranged in a write head carrier that is large in area in comparison tothe write head, with which the heating time is reduced, with which areliable regulation is guaranteed, that also only requires a low spacerequirement for heating elements and, as needed, sensor elements, andthat can also be mounted with low outlay.

This object is achieved by a heating device of the type described abovefor warming the ink in the write head of an ink printer comprising avoltage regulator serving as a heating element and a temperature sensorelement arranged on the write head carrier, the voltage regulator andthe temperature sensor element being connected to a regulating circuit;the heating element being supplied with a constant load current via theregulating circuit until an operating temperature is reached; and thedissipated power of the heating element warming the write head carrierand the ink in the write head to an operating temperature.

The heating device is further characterized by the heating element beingarranged in a housing having a low heat transmission resistance. In apreferred embodiment, the heating device is used on a printer having aplurality of write heads on the write head carrier, and the heatingelement and the temperature sensor element are arranged on the writehead carrier shared in common by all write heads and are connected tothe common regulating circuit.

The invention shall be set forth below with reference to the drawings.Shown therein are:

FIG. 1 is a schematic illustration of the arrangement of the heatingelement inventively employed and of the sensor element on the carrierfor the write head together with a regulating circuit;

FIGS. 2a and 2b are graphs of the curve of the load current of aninventively employed heating element as well as the curve of thetemperature dependent on the time;

FIG. 3 is an enlarged cross section of an example of the arrangement ofthe inventively employed heating element as well as of a sensor elementin a printer means comprising a plurality of write heads.

The example illustrated in FIG. I only shows the details necessary foran understanding of the invention, namely a write head 1 with exitnozzles 2 from which individual ink droplets are ejected by individuallydriven electrothermal transducer elements that respectively act on theink in the ink channels 3. This is based on the principle that hasbecome notoriously known in the meantime wherein an ink vapor bubble(referred to as a bubble) that effects a droplet ejection arises on thebasis of a controlled heating of the electrothermal transducer elementin the appertaining ink channel. This principle has therefore becomeknown by the name of the bubble jet method. The individual ink channels3 are in communication with a common ink chamber 4. Such write heads canbe constructed in what is referred to as thin-film technology, wherebythe electrothermal transducer, usually a heating resistor, and thecontacting for this heating resistor are constructed in layers on asubstrate carrier given simultaneously fashioning of the ink chamber 4and of the ink channels 3.

Corresponding to the demands cited at the outset, in accord wherewithcare must be exercised for an adequate cooling during the printing modegiven employment of electrothermal transducers as drive elements for thedroplet ejection, the write head 1 is arranged on a relativelylarge-area write head carrier 5 acting as the cooling member. This isusually composed of aluminum.

The heating element 6 provided for warming the ink is arranged on thewrite head carrier 5, as is the sensor element 7. In accord with theinvention, what is a component part of a voltage regulator is employedas their heating element 6 and its dissipated power is exploited for itsheating capacity to warm the write head carrier 5. Voltage regulatorsand their components are intrinsically known. An integrated circuit inwhich a thermal overload protection that protects the circuit as well asthe overall arrangement against destruction or, respectively, burn-up iscontained is preferably employed for this purpose. A PTC resistor thatis likewise intrinsically known is preferably employed as the sensorelement 7. The application of the heating element and of the sensorelement on the write head carrier 5 presents no design problems. Incooperation with a regulating circuit 8 that is connected to the heatingelement 6 and to the sensor element 7 via the terminals 9, noticeablyshorter heat-up times for the ink derive than with PTC resistor heatingelements of the prior art.

The regulating circuit 8 recited as an example is essentially composedof a first voltage divider having the fixed resistors 10 and 11, of asecond voltage divider that contains the sensor element 7 as a furtherresistor in addition to a fixed resistor 12, of a differential amplifier13 whose inputs are connected to the taps of the first and of the secondvoltage divider, as well as of a transistor output stage 14 and of avariable resistor 15 with which the load current IL of the heatingelement 6 is set. Further component parts (resistors and capacitors) ofthe regulating circuit 8 are not referenced in detail.

The operation of the arrangement is essentially as follows. Below adefined ink temperature that is referred to below as an operatingtemperature Tb and that usually amounts to 35° C., the output transistor14 is transmissive via the output of the differential amplifier 13 andthe heating element 6 is thus supplied with the full load current IL.The setting of the current IL and, thus, the setting of the heatingenergy as well ensues via the resistor 15. In practical operation, aload current IL=0.8 A occurs. The response threshold of the regulatingcircuit 8 can be set via the resistor 12 in cooperation with the sensorelement 7. When the predetermined operating temperature Tb is reached,then the output transistor is turned off via the output of thedifferential amplifier 13. The dissipated heat arising during the activephase of the voltage regulator component 6 and that is constant duringthis phase due to the regulator properties of the voltage regulatorcomponent 6 leads to a rapid heating of the aluminum carrier 5 and,thus, of the ink in the ink chamber 4 and in the ink channels 3 as well.A heating capacity up to 25 W can be achieved with the voltage regulatorserving as the heating element 6. The housing of such a voltageregulator component also has an extremely low heat transmissionresistance, this likewise having an extremely beneficial influence onthe reduction of the heat-up time.

The advantage involved with the employment of a voltage regulator as theheating element 6 may be seen from FIGS. 2a and 2b. The solid line inFIG. 2a shows the curve of the load current IL and the solid line inFIG. 2b shows the curve of the temperature T dependent on the time t.For comparison, the current curve and the temperature curve givenemployment of heating element's of the prior art (PTC resistor), areentered as broken lines in FIGS. 2a and 2b. Given employment of a PTCresistor, one can see that a high current first flows upon turn-on(IL=IA) but this drops to a low value FIG. 2a shortly thereafter whenthe reference temperature for the PTC resistor is reached. A heat-uptime th2 FIG. 2b thus derives until the operating temperature Tb (forexample, Tb=35° C.) is reached proceeding from an initial temperature Ta(for example, Ta=10° C.). Given employment of the heating element of theinvention, the load current IL (IL=0.8A) constantly remains at a highvalue FIG. 2a until the required operating temperature Tb is reached.The heat-up time is thereby considerably shorter and the operatingtemperature Tb is already achieved at time thl FIG. 2b.

The arrangement can be advantageously utilized in ink printer equipmenthaving a plurality of write heads, for example in what are referred toas multi-color printer means. Since the inventively employed heatingelement can output a high heating capacity and itself has only a lowthermal resistance, it can be arranged on the common write head carrierfor the write heads together with the sensor element. This has theadvantage that a single heating element is adequate for heating the inkof a multitude of write heads and that only a single regulating circuitneed be provided as well.

FIG. 3 shows an example of this design. The printer means in thisexample is composed of four write heads 16 through 19 for which a commonwrite head carrier 20 that can again be an aluminum carrier is providedas cooling member. The heating element 6 and the sensor element 7 arearranged thereon. Differing from the illustration of FIG. 1 wherein anarrangement is shown in plan view, FIG. 3 represents a sectional view,i.e. the ink channels 21 in each of the write heads 16 through 19 lie inthe plane of the drawing here. The regulating circuit 8 set forth withreference to FIG. 1 is also utilized, for example, in this embodiment.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

We claim:
 1. A write head of an ink printer including a device forwarming ink, the write head comprising:a plurality of ink channelsending in discharge openings in the write head, individually drivable,electrothermal transducer elements as first heating elements allocatedto every ink channel under whose influence the ink in a region of atransducer element in the ink channel is suddenly heated until an inkvapor bubble is formed, a write head carrier on which the write head isarranged that is large in area in comparison to the write head, atemperature sensor element mounted on the write head carrier, aregulating circuit means for producing a substantially constant loadcurrent to the write head, an additional heating element being acomponent part of a voltage regulator connected directly across supplyleads of the regulating circuit, the additional heating element being anintegrated circuit mounted in thermally conductive fashion on the writehead carrier together with the temperature sensor element, saidintegrated circuit being operable at an active phase to regulate voltageacross the supply leads and to simultaneously dissipate heat; and meansfor connecting the additional heating element to receive the constantload current from the regulating circuit means until an operatingtemperature is reached as a result of dissipated heat of the additionalheating element warming the write head carrier and the ink in the writehead to the operating temperature.
 2. A write head according to claim 1,further comprising:a housing for the integrated circuit having a lowheat transmission resistance and mounted on the write head carrier totransmit heat from said additional heating element to said write headcarrier.
 3. A write head according to claim 1, whereinsaid write headcomprises a plurality of write heads, the write head carrier beingshared in common by all of said plurality of write heads, and saidadditional heating element and said temperature sensor element are inthermal contact with all of said plurality of write heads.